<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title></title>
    <script type="text/javascript">
    /*
    let show = function(a){
      return a*2;
    };

    let show = (a)=>{
      return a*2;
    };

    let show = a=>{
      return a*2;
    };
        */
    let show = a=>a*2;
    alert(show(12));
    </script>
  </head>
  <body>

  </body>
</html>
